New, Generalized Criteria for Determining the Level of Underbalance for Obtaining Clean Perforations

Abstract

ABSTRACT: New criteria for estimating underbalance requirements for obtaining clean perforations are presented. These criteria are based on analysis of flow velocities and pressure gradients in the near wellbore region at early times using finite element method, existing field data and a physical model of perforation cleanup. The results indicate that the required level of underbalance is one that will introduce non-Darcy effects in the vicinity of perforations at early times. Simple equations based on pseudosteady-state, radial and turbulent flow in the crushed zone have been presented to approximate the required level of underbalance for a given set of formation and fluid properties.